1. Field of the Invention
The invention relates generally to electrical switching apparatus and, more particularly, to gassing insulators for the arc chute assemblies of electrical switching apparatus, such as circuit breakers. The invention also relates to arc chute assemblies for electrical switching apparatus. The invention further relates to electrical switching apparatus employing arc chute assemblies.
2. Background Information
Electrical switching apparatus, such as circuit breakers, provide protection for electrical systems from electrical fault conditions such as, for example, current overloads, short circuits, and abnormal level voltage conditions.
Circuit breakers, for example, typically include a set of stationary electrical contacts and a set of movable electrical contacts. The stationary and movable electrical contacts are in physical and electrical contact with one another when it is desired that the circuit breaker energize a power circuit. When it is desired to interrupt the power circuit, the movable contacts and stationary contacts are separated. Upon initial separation of the movable contacts away from the stationary contacts, an electrical arc is formed in the space between the contacts. The arc provides a means for smoothly transitioning from a closed circuit to an open circuit, but produces a number of challenges to the circuit breaker designer. Among them is the fact that the arc results in the undesirable flow of electrical current through the circuit breaker to the load. Additionally, the arc, which extends between the contacts, often results in vaporization or sublimation of the contact material itself. Therefore, it is desirable to extinguish any such arcs as soon as possible upon their propagation.
To facilitate this process, circuit breakers typically include arc chute assemblies which are structured to attract and break-up the arcs. Specifically, the movable contacts of the circuit breaker are mounted on arms that are contained in a pivoting assembly which pivots the movable contacts past or through arc chutes as they move into and out of electrical contact with the stationary contacts. Each arc chute includes a plurality of spaced apart arc plates mounted in a wrapper. As the movable contact is moved away from the stationary contact, the movable contact moves past the ends of the arc plates, with the arc being magnetically drawn toward and between the arc plates. The arc plates are electrically insulated from one another such that the arc is broken-up and extinguished by the arc plates. Examples of arc chutes are disclosed in U.S. Pat. Nos. 7,034,242; 6,703,576; and 6,297,465.
Additionally, along with the generation of the arc itself, ionized gases, which can cause excessive heat and additional arcing and, therefore, are harmful to electrical components, are formed as a byproduct of the arcing event. The ionized gases can undesirably cause the arc to bypass a number of intermediate arc plates as it moves through the arc chute. This reduces the number of arc voltage drops and the effectiveness of the arc chute. It also creates current and gas flow patterns that tend to collapse groups of arc plates together, further reducing the voltage divisions in the arc chute and its cooling effectiveness. Additionally, debris, such as, for example, molten metal particles, are created during the arcing event and can collect in the gaps between arc plates, causing an electrical short, and high current levels during current interruption generate high magnetic forces, which attract the arc plates together.
There is a need, therefore, to provide sufficient mechanical support and electrical insulation between the arc plates of the arc chute assembly.
Accordingly, there is room for improvement in arc gassing insulators for arc chute assemblies, and in arc chute assemblies for electrical switching apparatus, such as circuit breakers.